This invention relates generally to switches, to electronic switches, and particularly to bidirectional, or alternating current (AC), switches for use in or with a variety of electric circuits notably including matrix converters and AC power supplies.
Perhaps the most familiar example of AC switches is a bidirectional triode thyristor, better known as TRIAC (TRIode for Alternating Current). The TRIAC has the weakness that, once triggered, it cannot be turned off at a controllable point in an AC cycle; rather, it remains conductive until the current flowing therethrough drops below a predetermined threshold.
Some bidirectional switching devices have been known which meet that requirement. One of them (shown in FIG. 1 of the drawings attached hereto) comprises two insulated-gate bipolar transistors (IGBTs) connected in inverse series with each other and two diodes connected in inverse parallel with the respective IGBTs. The two IGBTs are replaceable with insulated-gate or junction field-effect transistors or bipolar transistors. A further known bidirectional switch is an inverse parallel connection of two IGBTs
These prior art bidirectional switching circuits, all incorporating normally-off solid-state switches, are alike in being unnecessarily complex in construction and high in turn-on resistance and voltage. Moreover, being made from semiconducting silicon materials with relatively low bandgaps, such known devices are not so high in antivoltage strength as can be desired.
WO 2004/114508 (FIG. 2) teaches a bidirectional switching device expressly designed to defeat all the noted drawbacks of the more conventional devices above. This prior art device offers the benefits of greater simplicity in construction and a higher antivoltage strength, the latter being a result of the fact that its semiconductor switch, the primary component, is made from a semiconducting compound such as, typically, nitride. Offsetting these benefits are its bulkiness and high manufacturing costs resulting from use of some unnecessarily self-contained components that are essential for its functioning. Difficulties have also been experienced in providing a reference potential needed for gating. The noted prior art devices with there inherent problems will be explained later in some more detail with reference to the attached drawings.